work without permissions to create unpacked_bin

[avh4]

From stoeffel/elmi-to-json#20 (comment), the issue seems to be that $NODE_HOME/<package name> is owned by root, but then the install script (or the wrapper script itself if you install with scripts disabled) can't create a folder there (and also couldn't download or modify files there).

The planned fix is that if it doesn't have write access there then it should fallback to unpacking the binaries to ${XDG_CACHE_HOME:-$HOME/.cache}/<package name>-binwrap/